Meeting Abstract
Urbanization has altered the biotic integrity of urban streams. Impervious surface cover in cities decreases the fraction of precipitation that enters groundwater. Thus surface run-off is much greater following precipitation and urban stream flows and temperatures can change rapidly. This loss of groundwater can also produce lower flows in urban streams between precipitation events which alters natural thermal regimes. Urban fishes have been increasingly exposed to these changes of flow and temperature over the past 200 years. Interestingly, these changes to the hydrologic regime wrought by urbanization are identical to the changes expected from climate disruption in many regions. The blacknose dace (Rhinichthys atratulus) is an urban-tolerant species that exists in some of the most degraded streams around Baltimore, often to the point of being the only fish species left in a stream, yet this fish is also abundant in nearby, rural stream communities with diverse fish faunas. This gradient of urbanized streams at similar latitude, altitude and stream order, sets up an intraspecific comparative experiment from which one can test hypotheses concerning how urbanization has changed this species. Swimming performance of blacknose dace is highly predicated by the stream baseflow from where they are captured, but dace from urban streams are better sprinters and have greater endurance performance than predicted; training and de-training studies implicate phenotypic plasticity for these results. Thermal tolerance in dace is strongly determined by acclimation temperature and experiments are so far suggestive of urban fish having more plastic thermal tolerance and having their swimming performance less affected by pulses of temperature.
